This invention relates to inkjet printing devices, and more particularly to an inkjet printing device that includes a printhead portion that receives drop activation signals for selectively ejecting ink.
Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates each of a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators.
Individual drop generators are selectively activated by the use of an activation signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing.
The electric current is frequently provided to individual resistors or drop generators by a switching device such as a field effect transistor (FET). The switching device is activated by a control signal that is provided to the control terminal of the switching device. Once activated the switching device enables the electric current to pass to the selected resistor. The electric current or drive current provided to each resistor is sometimes referred to as a drive current signal. The control signal for selectively activating the switching device associated with each resistor is sometimes referred to as an address signal.
In one previously used arrangement, a switching transistor is connected in series with each resistor. When active, the switching transistor allows a drive current to pass through each of the resistor and switching transistor. The resistor and switching transistor together form a drop generator. A plurality of these drop generators are then arranged in a logical two-dimensional array of drop generators having rows and columns. Each column of drop generators in the array are connected to a different source of drive current and with each drop generator within each column connected in a parallel connection between the source of drive current for that column. Each row of drop generators within the array is connected to a different address signal with each drop generator within each row connected to a common source of address signals for that row of drop generators. In this manner, any individual drop generator within the two-dimensional array of drop generators can be individually activated by activating the address signal corresponding to the drop generator of row and providing drive current from the source of drive current associated with the drop generator column. In this manner, the number of electrical interconnects required for the printhead is greatly reduced over providing drive and control signals for each individual drop generator associated with the printhead.
While the row and column addressing scheme previously discussed is capable of being implemented in relatively simple and relatively inexpensive technology tending to reduce printhead manufacturing costs, this technique suffers from the disadvantage of requiring relatively large number of bond pads for printheads having large numbers of drop generators. For printheads having in excess of three hundred drop generators, a number of bond pads tend to become a limiting factor when attempting to minimize the die size.
Another technique that has been previously been used makes use of transferring activation information to the printhead in a serial format. This drop generator activation information is rearranged using shift registers so that the proper drop generators can be activated. This technique, while greatly reducing the number of electrical interconnects, tends to require various logic functions as well as static memory elements. Printheads having various logic functions and memory elements require suitable technologies such as CMOS technology and tend to require a constant power supply. Printheads formed using CMOS technology tend to be more costly to manufacture than printheads using NMOS technology. The CMOS manufacturing process is a more complex manufacturing process than the NMOS manufacturing process that requires more masking steps that tend to increase the costs of the printhead. In addition, the requirement of a constant power supply tends to increase the cost of the printing device that must supply this constant power supply voltage to the printhead.
There is an ever present need for inkjet printheads that have fewer electrical interconnects between the printhead and the printing device thereby tending to reduce the overall costs of the printing system as well as the printhead itself. These printheads should be capable of being manufactured using a relatively inexpensive manufacturing technology that allows the printheads to be manufactured using high volume manufacturing techniques and have relatively low manufacturing costs. These printheads should allow information to be transferred between the printing device and the printhead in a reliable manner thereby allowing high print quality as well as reliable operation. Finally, these printheads should be capable of supporting large numbers of drop generators to provide printing systems that are capable of providing high print rates.
One aspect of the present invention is an inkjet printhead having a plurality of drop generators responsive to drive current and address signals for dispensing ink. The inkjet printhead includes first and second drop generators disposed on the printhead with each of the first and second drop generators configured to receive drive current from a drive current source. Each of the first and second drop generators is configured to receive address signals from a common address source. The inkjet printhead further includes a first switching device connected between the common address source and each of the first and second drop generators. The first switching device is responsive to enable signals for selectively providing the address signal to only one of the first and second drop generators.
Another aspect of the present invention is that the first drop generator includes a second switching device connected between a pair of drive current conductors coupled to the source of drive current. The second switching device is responsive to address active signals for selectively activating the first drop generator. Included with the second drop generator is a third switching device connected between a pair of drive current conductors coupled to the source of drive current. The third switching device is responsive to address active signals for selectively activating the second drop generator.
Yet another aspect of the present invention is that the first switching device includes a fourth and fifth switching device. The fourth switching device is connected between the source of address signals and the second switching device and the fifth switching device is connected between the source of address signals and the third switching device. The fourth switching device is responsive to enable signals for selectively providing address signals to the second switching device. The fifth switching device is responsive to enable signals for selectively providing address signals to the third switching device.